ES2549182T3 - Self-adjusting and self-adjusting intervertebral disc prosthesis - Google Patents

Abstract

Intervertebral disc prosthesis (1) comprising at least three pieces, among which a first plate of said upper plate (2) that has an upper face (22) that has a convex profile in the sagittal plane of the prosthesis, a second plate of said lower plate (3) that includes a lower face (32) that has a flat profile in the sagittal plane of the prosthesis, and a mobile nucleus (4) arranged between said plates (2,3), the nucleus having movable (4) an upper concave surface (44) in congruent contact with the convex surface (26) arranged on the lower surface (25) of the upper plate (2) and a lower convex surface (45) in congruent contact with the surface concave (36) arranged on the upper surface (35) of the lower plate (3), each of said surfaces being determined by a different radius of curvature, the radius of curvature of the concave surface (44) of the core being lower than the of its convex surface (45), and The centers of said concave (44) and convex (45) surfaces being located on the axis of radial symmetry of the central nucleus and placed on the same side of the prosthesis (1), the upper plate (2) being characterized in that the plate The bottom (3) includes stops in at least the two lateral-lateral and antero-posterior directions, these stops are obtained by means of a peripheral edge (37) made on the upper face (25) of said lower plate (3) around the concave surface (36), or characterized in that the upper plate (2) has stops in at least the two lateral-lateral and antero-posterior directions, the stops are obtained thanks to a groove (27) made on the lower face (25) around its convex surface (26).

Description

Self-adjusting and self-adjusting intervertebral disc prosthesis

The present invention relates to an intervertebral disc prosthesis intended to replace the cartilaginous fibro 5 discs ensuring the union between the vertebrae of the spine, and more specifically at the level of the cervical spine.

In this area, a large number of previous prostheses have already been performed. However, a part of these prostheses may cause undesirable effects in patients provided with said prostheses. In fact, if they are constructed with a material that is too compressible, or if they allow the different pieces that constitute said prostheses to have a movement that is too important with respect to each other, there is a risk of projection of less a part of the prosthesis outwards of the vertebrae. In addition, the literature describes that most of these prostheses do not correctly reproduce the kinematics of the vertebral unit with a progressive segmental kyphosis positioning explaining the limitations of the loads exerted on the 15 posterior inter-apophyseal joints (commonly called posterior articulations), which implies a high risk of developing osteoarthritis at the level of these posterior joints. The main difficulty is to control the relative movements of the different pieces that constitute these prostheses.

It should be remembered that the vertebral functional unit (UFV) is a complex system that integrates the intervertebral disc, the posterior joints and the musculoskeletal system. This complex system does not have any horizontal transverse symmetry plan: in fact, at the anatomical level, in the sagittal plane, the contour of the inferior surface of the underlying vertebra has a concave trough shape, while the contour of the upper surface of The underlying vertebra is globally flat. The cavity of the inferior surface of the underlying vertebra is well marked at the level of the cervical vertebrae, while it is less pronounced at the level of the lumbar. The intervertebral disc between these two surfaces thus presents no horizontal transverse symmetry.

When this unit is integrated into a set, the sagittal equilibrium minimizes the tensions on the Posterior Ligation System, and as a consequence on the functional unit, contributing to define the Neutral Zone 30 (mobility zone that does not imply any intrinsic mechanical resistance of the different elements).

Degenerative pathology is the result of a loss of physiological disc stiffness. Mobility is resolved in an elementary movement, in particular in translation, transforming the guide function of the articulants into a stop function. 35

Any intervertebral prosthesis will therefore have as a first requirement, not only to restore an amplitude of mobility but also to preserve or restore the neutral zone, that is, a physiological amplitude / neutral zone ratio. This ratio involves the notion of coherence of the CIR (instantaneous center of rotation) with those of the UFV.

 40

The second requirement is the control of the couplings, that is, the control of the articular load, as long as it refers to a pathological joint with an altered posterior ligament system, involving changes in the sagittal balance, and participating in the extension of the Neutral Zone. Therefore, a braking of the postero-anterior translation in flexion-extension is necessary, reducing the translation-rotation ratio, and inducing a self-centering by antero-posterior translation. The same principle for lateral inclination with an opposite translation induced by rotation.

In the prior art, intervertebral prostheses were already known, which comprise three pieces, of which a first plate is called an upper plate, a second plate is called a lower plate and a mobile core is disposed between said plates. The mobile core of these prostheses has a convex upper surface of 50 contact with the upper plate and with a concave lower surface of contact with the lower plate. Examples of such prostheses can be found in WO 2005/094737, WO 2006/105603, US 2007/270958 or US 2004/138753.

However, these known prostheses do not respond satisfactorily to the aforementioned requirements, in particular, they are not stable in the physiological compression situation. This defect will be explained in detail later in the description in relation to Figures 10, 10A, 11 and 11A.

The present invention therefore aims to alleviate certain disadvantages of the prior art, proposing a new type of intervertebral disc of simple conception, which allows controlling the movements of the different pieces that constitute said prosthesis in order to prevent the rear joints are subject to very important load requirements. In addition, the prosthesis according to the invention has a self-centering and self-stabilizing kinematics of the prosthetic elements, ensuring a physiological location of the instantaneous centers of rotation.

 65

In this regard, the present invention relates to an intervertebral disc prosthesis as defined by claim 1. This prosthesis comprises at least three pieces wherein a first plate called the upper plate comprises an upper face that has a convex profile in the Sagittal plane of the prosthesis, a second plate called the lower plate that involves a lower face that has a flat profile in the sagittal plane of the prosthesis, and a mobile core arranged between said plates. 5

In this prosthesis it should be noted that the mobile core has a concave upper surface in congruent contact with the convex surface disposed on the lower surface of the upper plate and a convex lower surface in congruent contact with the concave surface disposed on the upper surface of the plate lower, each of said surfaces being determined by a different radius of curvature, the radius of curvature 10 of the concave surface of the core being lower than that of its convex surface, the centers of said concave and convex surfaces being located on the axis of radial symmetry of the central nucleus and placed on the same side of the prosthesis, those of the upper plate.

The disc prosthesis of the present invention has three components provided with concave and convex surfaces. 15 To respond to the physiological limitations set forth above, the arrangement of these concave and convex surfaces is specific and their investment is not feasible due to the considerable advantages provided by this specific configuration, as will be explained later in detail.

The following describes, by way of non-limiting example, a preferred embodiment of the prosthesis according to the invention, with reference to the drawings in the annex, in which:

- Figure 1 is a front perspective view of the prosthesis mounted according to an upper 3/4 angle,

- Figure 2 is a rear perspective view of the prosthesis mounted according to an upper 3/4 angle,

- Figure 3 is an exploded perspective front view according to an upper 3/4 angle, 25

- Figure 4 is a partial sectional view in the sagittal plane of the prosthesis,

- Figure 5 is a schematic view similar to Figure 4 depicting a first variant of the prosthesis with stops,

- Figure 6 is a schematic view similar to Figure 4, which represents a second variant of the prosthesis with stops, 30

- Figure 7 is a schematic view similar to Figure 4 depicting the compensation of the displacements of the different elements of the prosthesis in a flexion-extension situation,

- Figure 8 is a schematic view similar to Figure 4 depicting the compensation of the displacements of the different elements of the prosthesis in a pure translational situation,

- Figure 9 is a schematic view similar to Figure 4 depicting the location of the instantaneous center of rotation of the prosthesis in flexion situation;

- Figures 10 and 10A are respectively a partial sectional view and a schematic view in the sagittal plane of a prosthesis according to the prior art, wherein the convexity radius of the lower plate is greater than the concavity radius of the upper plate, for Figure 10A said prosthesis being represented at rest, with full strokes, and under the effect of compression, with dots; 40

- Figures 11 and 11A are respectively a partial sectional view and a schematic view in the sagittal plane of a prosthesis according to the prior art, wherein the convexity radius of the lower plate is less than the concavity radius of the upper plate, for Figure 11A, said prosthesis being represented at rest, with full strokes, and under the effect of compression, with dots;

- Figures 12 and 12A are respectively a partial sectional view and a schematic view in the sagittal plane 45 of the prosthesis according to the invention, for Figure 12A, said prosthesis being represented at rest, with full strokes, and under the effect of a compression, with points.

Referring to Figures 1 to 4, the intervertebral disc prosthesis 1, according to the invention, comprises at least three pieces, of which a first plate called upper plate 2, a second plate called lower plate 3, and a core mobile 4, arranged between the two plates 2, 3, the upper plate 2 and the lower plate 3 being articulated, one in relation to the other.

Thus, the upper plate 2 comprises a completely flat central body 21, whose shape and dimensions correspond to those of the lower surface of the cervical spine vertebra located above said upper plate 55 2. In order to adapt to said vertebra and allowing the fastening of said upper plate 2 at bone level, the upper face 22 of said central body 21 has a convex profile according to the slightly pumped sagittal plane. Preferably, the profile according to the frontal plane of this upper face 22 is also convex. The profile in the frontal plane may also be completely flat: the specialist technician will adapt the profile of the outer upper face 22 of the upper plate 2 to fit the anatomical contour of the associated articular surface, depending on the positioning along of the spine.

Moreover, this upper face 22 is provided with fastening means 23. In a preferred embodiment, the fastening means 23 are teeth 24 that exit perpendicularly from said upper face 22, substantially parallel to each other, perpendicular to the plane. Sagittal prosthesis 1. The section of these teeth 24 65 has a general form of regular trapezius. The upper plate 2 also includes at least a part of the lower face 25 of said central body 21, a convex surface 26, preferably in the form of a spherical cap disposed in the vicinity of the center of said lower face 25.

Similarly, the lower plate 3 comprises a completely flat central body 31, whose shape and 5 dimensions correspond to those of the upper surface of the vertebra of the cervical spine located under said lower plate 3. In order to adapt well to said vertebra underlying and allowing the fastening of said lower plate 3 with the bone medium, the lower face 32 of said central body 31 has a flat sagittal profile. Preferably, the profile of the lower face 32 in the frontal plane is equally flat. The profile in the frontal plane may also be convex, with a slight pumping: the specialist technician will adapt the profile of the outer lower face 32 of the lower plate 10 3 to fit the anatomical contour of the associated articular surface, depending on the positioning along the spine.

On the other hand, this external lower face 32 is provided with fastening means 33. In a preferred embodiment, the fastening means 33 are teeth 34 similar to the teeth 24 of the upper plate 2, described 15 above, implanted. perpendicular to the sagittal plane of the prosthesis 1. The lower plate 3 also includes at least a part of the upper face 35 of said central body 31, a concave surface 36, preferably in the form of a spherical cap disposed in the vicinity of the center of said upper face 35.

In order to improve the contact and clamping in the bone of the teeth 24, 34, it is possible, for example, to use an interface 20 of the hydroxyapatite type.

The mobile core 4 comprises an upper face 41, a lower face 42 and a peripheral face 43 that joins the upper and lower faces 41, 42 together. In a preferred embodiment, this peripheral face 43 has a generally frustoconical shape. 25

To obtain an articulation between the upper plate 2 and the lower plate 3 around the mobile core 4, it is understood that the upper plate 2, the lower plate 3 and the mobile core 4 must be such that the upper face 41 of the mobile core 4 is in congruent contact with the convex surface 26 of the lower face 25 of the upper plate 2, and that the lower face 42 of the movable core 4 is in congruent contact with the concave surface 36 of 30 the upper face 35 of the lower plate 3 Such a configuration allows a relative displacement between the upper and lower plates 2,3 and the mobile core 4.

To achieve this, the movable core 4 comprises, on the one hand, on at least a part of its upper face 41, a spherical concave face 44 of a radius of curvature substantially equal to that of the convex surface 26 of the lower surface 25 of the upper plate 2, and, on the other hand, on at least a part of its lower face 41, a spherical convex surface 45 with a radius of curvature substantially equal to that of the concave surface 36 of the upper surface 35 of the plate bottom 3.

In a preferred embodiment, the concave surface 44 and the convex surface 45 respectively cover the entire upper face 41 and the lower face 42 of the movable core 4.

In addition, the mobile core 4 preferably has a radial symmetry axis, so that it has the centers of the curvature rays of its upper and lower faces 41, 42, located on said axis of symmetry and placed on the same side of the prosthesis, namely that of the upper plate 2. 45

Finally, the radius of curvature of the lower face 42 is greater than that of the upper face 41 and the distance between the centers of the radii of curvature, conditioned by the intervertebral space, is advantageously as small as possible.

 fifty

The specialist technician will have no difficulty in dimensioning said radii of curvature, and consequently, in obtaining relative displacement speeds of the different constituent elements of the prosthesis 1, allowing said prosthesis 1 to be self-adaptable and self-stable. It is also well understood that said radii can be variable depending on the position of the prosthesis 1 along the spine since the relative travel speeds are also a function of said position. 55

According to a first embodiment variant and in reference to Figure 5, in order to limit the risk of projection of at least one part of the prosthesis 1 and the clearance of one plate in relation to the other, the upper plate 2 in the periphery of its convex surface 26 on its lower face 25, stops in at least the two antero-lateral and antero-posterior directions in relation to the positioning of the prosthesis 1 on the spine. These 60 stops are advantageously obtained thanks to a throat 27 formed on the lower face 25 around its spherical convex surface 26.

Similarly, with reference to FIG. 6, according to a second variant embodiment, the lower plate 3 has, at the periphery of its concave surface 36 on its upper face 35, stops in at least the two lateral-lateral directions. and anteroposterior in relation to the positioning of the prosthesis 1 on the spine. These stops are advantageously obtained by means of a peripheral flange 37 made on the upper face 35 around its spherical concave surface 36.

The particular configuration of the prosthesis allows the self-centering of the mobile core 4 and the self-adaptation of the 5 prostheses 1 in order to respect the natural physiological kinematics of the cervical spine.

Indeed, in reference to Figures 7 and 8, which respectively represent the prosthesis 1 that has undergone a deformation of flexion-extension and pure translation, when the cervical spine movement takes place and under the action of the transmitted forces by the adjacent vertebrae, the prosthesis 1 passes, for example, from a resting position, represented with a strong line on the figure, to a working position, represented by dotted lines in the figure. It is well understood then, that the mobile core 4, when it is displaced, will compensate for the displacement of the upper plate 2 in relation to the lower plate 3. The prosthesis 1 according to the invention, thus allows a control and limitation of the efforts exerted on the anterior and posterior joints thereby avoiding hyperpressure problems. fifteen

In addition, referring to figure 9, the instantaneous rotation centers (CIR) of the prosthetic assembly inserted in the intervertebral joint are therefore located in the physiological cloud, which is extension flexion (case of figure 9) or lateral inflection (not drawn).

 twenty

Referring to Figure 9, the determination of the CIR is carried out as follows: A and B are 2 points belonging to the top plate. The C.I.R. of the upper plate is located at the intersection of the perpendicular at the speeds of these two points (in relation to the lower plate). Consequently the nucleus will be designated by the letter n, the lower plate by the letters pi and the upper plate by the letters ps.

 25

When the speed of A / lower plate (V (A / pi)) is perpendicular to OA, the C.I.R. It is, therefore, about OA.

The speed of B / bottom plate is composed of the drag speed Ve (B) = V (A / pi) = OA x ω (n / pi) and the relative speed perpendicular to AB, Vr (B) = AB x ω (ps / pi).

Therefore, we have that V (B) / pi) = Ve (B) + Vr (B). 30

The C.I.R. it is at the intersection of OA and the perpendicular in B to V (B / pi).

Although in this configuration, the centers of rotation of the mechanical components are above the upper plate, there is coherence between the prosthetic CIRs and those of the Functional Vertebral Unit. 35

Figures 10, 10A and 11, 11A demonstrate the overall physiological instability of known prostheses of the prior type, disclosed in WO 2005/094737, WO 2006/105603, US 2007/270958 or US 2004/138753, either with a radius of curvature of the convexity of the lower plate larger (figures 11,11A) or smaller (figures 10, 10A) than the radius of curvature of the concavity of the upper plate. 40

The core travels around the center O of the convexity of the lower plate and the upper plate moves around the center A of the convexity of the upper surface of the core.

In the case of the arrangement of Figures 10,10A, when the loading of the upper plate in its half B takes place, the center A travels around and above the center O, and the point B moves around and by above center A and nothing prevents displacement from point B around center A and center A around center O without being able to spontaneously return to their original position. Only the muscular actions allow to counteract this instability, dragging then a harmful joint overload and an energetic consumption. fifty

In the case of the arrangement of figures 11, 11A, when the loading of the upper plate in its half B takes place, the center A moves around and below the center O and the point B moves around and above the center A, and nothing prevents the movement from point B around center A from continuing without being able to spontaneously return to its original position. Only muscle actions allow this instability to be counteracted, thus dragging a damaging joint overload and energy consumption.

This instability of known prostheses is also found in the concept of biconvex or biconcave nucleus prostheses.

 60

With reference to Figures 12 and 12A, it will now be shown as contrary to known prostheses, the prosthesis according to the invention is dynamically stable.

In the prosthesis according to the invention, the concave-convex surfaces of the mobile core are reversed in relation to the known prior art: the upper plate has a convex spherical surface, the lower plate has a concave spherical surface, and the mobile core of Lenticular shape has spherical concave surfaces at the top and convex at the bottom.

The radius of curvature r of the concave upper surface of the core, congruent with the convex surface of the upper plate, is smaller than the radius of curvature R of its convex lower surface, which is congruent with the concave surface of the plate lower. The thickness of the nucleus is "e".

In this configuration (see figure 12A), the core always travels around the center O of the concavity of the lower plate, the center O being located above the core and the center A of the core concavity moving over a portion of the spherical surface of center O and radius OA = R - (r + e). When the loading of the top plate at its center B takes place, center A moves around and below center O, point B moves around and below center A, the system does not collapse and center A and point B can spontaneously return to their original position, without any joint overload and without energy consumption.

This concept that positions the center of rotation O of the core in relation to the lower plate, and the center of rotation 15 A of the upper plate in relation to the core above the upper plate, with A below O, ensures stability physiological of the prosthetic set.

According to another characteristic of the invention, the upper and lower plates 2, 3 and the mobile core 4, are advantageously constructed from non-metallic materials to allow MRIs to be performed in order to control especially the spinal cord. In this way, preferably, the upper and lower plates 2, 3 are made of polyetherketone, and the mobile core 4 is made of ceramic. These two materials also have the advantage of having a weak rubbing coefficient between them, which allows easy sliding of the pieces against each other and thus having a good articulation of the upper and lower plates 2, 3 on the core mobile 4. 25

The specialist technician will have no difficulty in sizing the different constituent elements of the prosthesis 1 according to the invention, especially respecting the minimum thicknesses attached to the nature of the materials used. For example, for the bottom plate 3 it will not decrease below 1.3 mm between the bottom of the concave shape 35 and the bottom face 32. 30

Furthermore, it is understood that according to the morphology of the patient and especially the intervertebral space, it is necessary to have a prosthesis 1 available in different dimensions. To play with the total height of the prosthesis 1, the thickness of the mobile core 4 and / or the thickness of the upper plate 2 will be modified.

 35

Finally, it is logical to think that the present invention is not limited to the example of the preferred embodiment and implementation described, and can be modified or adapted according to the particular needs or requirements without thereby departing from the scope of the invention.

Claims (8)

1. Intervertebral disc prostheses (1) comprising at least three pieces, among which a first plate of said upper plate (2) that comprises an upper face (22) having a convex profile in the sagittal plane of the prosthesis , a second plate of said lower plate (3) comprising a lower face (32) that 5 has a flat profile in the sagittal plane of the prosthesis, and a mobile core (4) disposed between said plates (2,3), the mobile core (4) comprising a concave upper surface (44) in congruent contact with the convex surface (26) disposed on the lower surface (25) of the upper plate (2) and a convex lower surface (45) in congruent contact with the concave surface (36) disposed on the upper surface (35) of the lower plate (3), each of said surfaces being determined by a different radius of curvature, 10 being the radius of curvature of the concave surface (44) of the nucleus inferior to that of its surface convex ce (45), the centers of said concave (44) and convex (45) surfaces being located on the axis of radial symmetry of the central core and positioned on the same side of the prosthesis (1), the upper plate being characterized (2) because the lower plate (3) has stops in at least the two lateral-lateral and anterior-posterior directions, these stops are obtained by means of a peripheral flange (37) made on the upper face (25) of said lower plate (3) around the concave surface (36), or characterized in that the upper plate (2) has stops in at least the two lateral and lateral directions, the stops are obtained thanks to a throat ( 27) made on the underside (25) around its convex surface (26). 2. Prosthetics (1) of the intervertebral disc, according to claim 1, characterized in that the upper plate (2) 20 comprises a central body (21) which comprises on its upper face (22) fastening means (23) and in the proximity of the center of its lower face (25) a convex surface (26) in the form of a spherical cap whose radius of curvature is substantially equal to that of the concave surface (44) of the mobile core (4), the fastening means (23 ) are trapezoidal teeth (24) parallel to each other, perpendicular to the sagittal plane of said prosthesis (1). 25 3. Prosthetics (1) of the intervertebral disc, according to any one of the preceding claims, characterized in that the lower plate (3) comprises a central body (31) which comprises fastening means (33) on its lower face (32). and, in the vicinity of the center of its upper face (35), a concave surface (36) in the form of a spherical cap whose radius of curvature is substantially equal to that of the convex surface (45) of the moving core (4), being the fastening means (33) trapezoidal teeth (34) parallel to each other, perpendicular to the sagittal plane of said prosthesis (1). 4. Prosthetics (1) of the intervertebral disc, according to any one of the preceding claims, characterized in that, the mobile core (4) comprises a peripheral face (43) in a generally frustoconical manner. 35 5. Prosthetics (1) of the intervertebral disc, according to any one of the preceding claims, characterized in that the lower plate (3) comprises a peripheral flange (37) made on the upper face (35) around the concave surface (36) , the mobile core (4) carrying a peripheral face (43) in a globally conical shape, which peripheral trunk face (43) ends in a stop against the peripheral flange (37) when the displacement of the core (4) takes place in relation to the bottom plate (3). 6. Prosthetics (1) of the intervertebral disc, according to any one of the preceding claims, characterized in that the upper plate (2) comprises a throat (27) made in the lower face (25) around its convex surface (26), the mobile core (4) carrying a peripheral face (43) of a globally conical shape 45, which peripheral trunk face (43) ends in a stop against the throat (27) when the displacement of the core (4) takes place in relation to the top plate (2). 7. Intervertebral disc prostheses (1) according to any one of the preceding claims, characterized in that the upper and lower plates (2,3) are constructed of polyether ketone. fifty 8. Intervertebral disc prostheses (1) according to any one of the preceding claims, characterized in that the mobile core (4) is constructed of ceramic.  55